ROLE OF RESPONSE REDUCTION FACTOR IN HIGHWAY BRIDGES

Abstract

The control of deformation is now a matter of contrast in seismic design philosophy instead of controlling large seismic forces. Undesirable inelastic deformation modes can be avoided by amplifying their strength in comparison to those obtained from the desirable inelastic modes. This leads designers to the capacity design philosophy. Capacity design requires design of suitable plastic hinges at suitable locations with adequate strength differential. Strength differential is created in the structure through the provision of response modification factor. In this report a detailed study has been summarized which imparts understanding of aspects of R- factor, influencing factors of R- factor and the dependency of R-factor on the structural component ductility. This dissertation has been carried out for judgement of response modification factor role in the design of highway bridge component. The emphasis has been given to the pier/bent of the bridge as is considered to be the best suited location in the bridge structure for plastic hinge formation. In the report two examples have been considered: (i) A bridge supported on a cantilever pier. (ii) A bridge supported on the-bent consisting of two piers. In both of the examples, verification of achieved ductility and R-factor has been brought about using Moment-Curvature (M-C) analysis and push over analysis. M-C analysis gives the component ductility and push over analysis gives the overall ductility achieved in the structure. In the 1St example two different configurations has been considered and design has been done using RDSO-2010 specifications. Achieved ductility and R-factor has been obtained only by M-C plot and effect of diameter has been studied. In the 2"d example the bent of the considered bridge has been designed with 4 different codes and the achieved ductility & R-factor have been evaluated using both M-C plot and push over analysis. The result has been compared for rigid and flexible foundation conditions. SAP2000 is used for M-C analysis and push over analysis.